The role of SQSTM1/p62 in Paget’s disease of bone (#63)

Paget’s disease of bone is characterised by localised areas of increased bone resorption and disorganised bone remodelling. This disorder is often inherited in an autosomal dominant fashion and displays high penetrance. In 2002 two groups published on the recurrent mutation of SQSTM1 in familial Paget’s. Cohort studies have shown that up to 50% of families harbour variants in this gene, with almost 30 different variants now associated with the disease. Most variants of SQSTM1/p62 associated with Paget’s affect the ubiquitin-associated domain of the protein and lead to reduced or abolished ubiquitin-binding ability. With one known exception, all Paget's variants also affect the ability of SQSTM1/p62 to provide negative feedback for the NF-kB transcription factor, activation of which is essential for osteoclast function. SQSTM1/p62 also regulates the oxidative stress response (Keap1/Nrf2), apoptosis and proteostasis. SQSTM1/p62 mediated protein degradation can be via either the proteasome or the lysosomal/autophagy pathway. SQSTM1/p62 is considered a signalling hub that links these cellular functions, primarily via autophagy. For instance, SQSTM1/p62 regulates various signalling intermediates and caspases in an autophagy dependent manner. Recently, many SQSTM1 variants have been linked with Frontotemporal dementia and motor neuron disease. Some of these variants were already associated with Paget’s. Initial functional characterisation of SQSTM1/p62 variants associated with these diseases have shown that some cause perturbations in oxidative stress responses, whereas others impact autophagy. This talk will summarize the role for SQSTM1/p62 variants in Paget’s disease of bone based on evidence from functional studies and animal models.